Question

In a mineral with chemical formula AT\(_4\)O\(_8\), the ionic radii of A and O are 1.12 Å and 1.40 Å, respectively. The coordination number of cation A is .........

Hint:

The coordination number of a cation is influenced by the ionic radius ratio between the cation and anion. Higher ratios usually correspond to a higher coordination number.

Answer 1

Correct Answer: 8

Step 1: Understanding coordination number.
The coordination number refers to the number of ions surrounding a central ion in a crystal structure. In this case, we are dealing with a mineral where the cation A is surrounded by anions O. The ionic radii of A and O are given, which can be used to calculate the coordination number of A.
Step 2: Determining the ratio of ionic radii.
The coordination number is typically related to the ratio of the radii of the cation and anion. In this case, the ionic radii are:
- The ionic radius of A = 1.12 Å,
- The ionic radius of O = 1.40 Å.
To calculate the coordination number, we look at the ratio of the ionic radii. The ideal coordination number is determined by this ratio. Typically, the coordination number increases as the cation-anion radius ratio increases.
Step 3: Applying the radius ratio.
For a cation-anion radius ratio between 0.4 and 0.7, the coordination number is typically 6. For a ratio above 0.7, the coordination number increases to 8. In this case, the ratio of 1.12 Å to 1.40 Å is approximately 0.8, which suggests a coordination number of 8 for cation A.
Step 4: Conclusion.
The coordination number of the cation A is 8.